In a vehicle transmission, hydraulically-actuated clutches are selectively applied to couple transmission input and output members in a desired speed ratio. A clutch-to-clutch shift occurs via a coordinated release of a clutch associated with the current speed ratio, i.e., the offgoing clutch, and engagement of another clutch associated with a desired new speed ratio, i.e., the oncoming clutch. Shifts in automatic transmissions, as well as in dual clutch transmissions and automated manual transmissions, are prompted by vehicle parameters, including throttle request and vehicle speed, the latter of which is affected by braking levels.
A typical vehicle control system includes an engine control module (ECM), which has overall authority for engine speed and torque functionality, and a transmission control module (TCM), which controls the functionality of the various clutches of the powertrain. The ECM is responsive to throttle level. The TCM, which is in communication with the ECM over a controller area network (CAN) bus, requests changes in engine speed from the ECM as part of its overall shift control function.